The next time your car is keyed, park it under a ray of sunshine. If your car is coated in a new polyurethane film developed by scientists from the University of Southern Mississippi, the scratch will be gone in an hour.

The research is detailed in the current issue of the journal Science.

"We have developed a new macromolecule," said Marek Urban, who, along with Biswajit Ghosh, wrote the paper. "When the polymer is damaged and exposed to sunlight, it is capable of repairing itself, and could be applied to many systems."

The new coating is 99.99 percent standard polyurethane, a material found in a wide range of products, including hard plastic and soft foams. The remaining 0.01 percent is either a four-molecule oxetane ring or a long rod of chitosan. Chitosan is closely related to chitin, the tough material found in the shells of lobsters and crabs.

When the polyurethane is damaged, a ring of oxetane is also ripped open. Breaking the surface of the polyurethane also allows ultraviolet light to enter the scratch, which breaks apart a rod of chitosan.

The broken chitosan rods and oxetane rings then bond with each other across the damaged area, dragging the two sides together to eliminate the scratch. If the polyurethane coating is left in the sun, a scratch heals itself in an hour.

Scientists say that the reaction only takes place when the surface is damaged, and that it should be should be able to repair most scratches indefinitely. But since the material is so new, they haven't been able to conduct long-term tests.